This disclosure relates generally to compositions and methods for treating a subterranean well prior to or during cementing operations. More specifically, the present disclosure relates to compositions and methods for cleaning casing and wellbore surfaces with fluids comprising a microemulsion.
Some statements may merely provide background information related to the present disclosure and may not constitute prior art.
The use of oil or synthetic-based drilling fluid (SBM/OBM) is widespread in many areas for a variety of reasons, including excellent shale inhibition, high rates of penetration and high lubricity. Oil- or synthetic-based drilling fluids generally comprise invert emulsion fluids, where the continuous or external phase is predominantly organic (e.g., mineral oil or synthetic oil), and the inverse or internal phase is usually aqueous (e.g., brines). The stability of invert emulsions is generally maintained by one or more additives present in the fluid, such as emulsifiers, emulsion stabilizing agents, and oil-wetting agents.
When drilling is performed with SBM/OBM fluids, the wellbore becomes oil-wet. Prior to cementing, the casing also becomes oil-wet while being run into the hole. This condition commonly results in poor bonding between the set cement and the casing and wellbore surfaces. Poor cement bonding may compromise the hydraulic seal in the annulus, potentially resulting in fluid communication between subterranean zones and potentially loss of the well integrity. Therefore, to ensure successful cementing, two conditions are necessary: (1) the SBM/OBM is effectively displaced and/or removed from the borehole; and (2) the wellbore-wall and casing surfaces are water-wet. Failure to satisfy Condition 1 may cause contamination of the cement slurry, and the cement performance may suffer. Failure to satisfy Condition 2 may lead to poor bonding between the cement and the borehole-wall and casing surfaces.
Despite efforts to prepare the borehole properly prior to cementing, Cement Bond Logs (CBL) commonly reveal poor or no bonding, or poor-quality cement behind casing. Current solutions to achieve mud removal and water wetting include pumping fluids that separate the cement slurry from the drilling fluid. The fluid may be a single-stage, viscous, water-base spacer that contains surfactants or a non-viscous (Newtonian) wash that contains surfactants; both having strong water-wetting tendencies. Or, a two-stage spacer system may be pumped that comprises base oil, solvents, or water-base chemical washes with surfactants, in combination with a viscous water-base spacer that contains water-wetting surfactants.
Proposals have been made in the art to use microemulsions for borehole preparation prior to cementing. See, for example, U.S. patents or applications U.S. Pat. Nos. 5,904,208; 7,380,606; 6,534,449; 7,392,844; 7,318,477; 7,481,273; 7,544,639; US2009/0008091; US2009/0221456; US 2008/0274918; and US 2008/0287324, all hereby incorporated by reference. Pertinent literature references to microemulsions include the following publications. Smith, G., Kumar, P. and Nguyen, D.: “Formulating Cleaning Products with Microemulsion”, paper number 164, Proceedings 6th World Congress CESIO, Berlin, Germany, Jun. 21-23, 2004; and Van Zanten, R., Lawrence, B., and Henzler, S.: “Using Surfactant Nanotechnology to Engineer Displacement Packages for Cementing Operations”, paper IADC/SPE 127885, 2010.